This invention relate generally to chemical treatment systems and more particularly for systems for effecting calibrated, proportional control of a chemical treatment system.
In the preferred technique for treatment of water (or some other liquid) with another liquid, e.g., a chemical, the chemical feed rate has to be established and must vary dynamically with the flow of water or other liquid that is to be treated. The ratio of treatment liquid to treated liquid is typically defined in Parts Per Million (PPM) and should remain constant at all flow rates so that results and cost are optimized. To accomplish that end, the technique known as "proportional feed" is utilized. The achievement of "proportional feed" has been accomplished typically by the use of a proportional loop-controller having an associated pump and flow meter.
In particular, the loop-controller system operates on the assumption that the chemical pump delivering the chemical from a storage tank is pumping the correct volume per stroke. Thus, tests must be run periodically to ensure that the system is working, is calibrated properly, and the tank or drum storing the testing chemical is not empty. While such operations are effective, they are nevertheless costly and labor intensive.
An alternative manner of effecting water treatment is to set the chemical pump feed rates at representative or average conditions, and thus not proportion the chemical feed rate to dynamic flow rates. Treating chemicals based on "average" conditions necessarily leads to overtreatment during some periods of time and undertreatment during other periods. Thus, while costs may not be excessive using this technique, the results frequently suffer. Yet another technique utilizes the feeding of excess chemical to handle the hightest flow rate. As will be evident, this technique leads to overfeed during some conditions. Thus, while the results of this technique are usually acceptable, the costs can be excessive. In view of the foregoing, it is generally accepted that proportional feed is the optimum treatment technique for most applications. To accomplish true "proportional feed", the feed rate of the treatment chemical must not only be varied directly with the treated liquid's (e.g. water) flow rate, but must also take into account changes in the pump's stroke volume, that is, the volumetric output of the pump.
It has been a practice in the past to manually calibrate the pump, that is, interrupt the treatment operation to determine the stroke output of the pump and then manually adjust the pump in the event that its output has deviated from a predetermined value. Obviously, such a manual technique is less than optimum.
It has also been suggested in the patent literature to control or calibrate a pump automatically. For example, in U.S. Pat. No. 4,322,972 (Karjala) there is disclosed a method and apparatus for the verification an calibration of pumping rates in systems having a volumetric pump drawing fluid from a tank. An effluent valve is connected to the base of the tank and the valve is, in turn, connected to the base of a calibrated column which is relatively small in cross sectional area compared to the tank. The liquid is drawn from the column during normal pumping operation as well as during a calibration cycle. When it is desired to measure the flow, the column is isolated from the storage tank by closing the tank's effluent outlet valve. After a specific period of time, e.g., a minute or more, the decrease in liquid level within the column is measured and the flow rate calculated. The effluent valve is then reopened without having disturbed the system or having turned off the pump, allowing the same pump or flow rate to continue. At this point, the operator of the system can adjust the pump to provide a different rate. It is also stated that the calibration method and apparatus can be automated.
U.S. Pat. No. 4,331,262 (Snyder, et al.) discloses an automatic fluid dispenser including a pump and counter means to count the number of incremental volumes. The volume of fluid delivered in the selected number of increments is determined either automatically or by an observer in a calibration procedure. A computer is provided to compare the volume of fluid delivered with the number of increments required to deliver that volume and to determine a "calibrated value" therefrom. This value is stored in the memory of the computer. Calibration means are provided to issue a command to the computer to store the calibrated value and controller means are provided for causing the fluid dispenser to deliver a selected volume of fluid either as a single dose or repetitively.
U.S. Pat. No. 2,826,067 (Braunlich) discloses testing apparatus for determining the delivery rate of a pulse type pump. The apparatus includes a calibration cylinder connected to the outlet of the pump through a valve. A float is provided in the column to provide a signal indicative of the rate of descent of liquid in the column, thereby indicating the pump rate. This signal is provided to a recorder to provide an indication of variations in the pump rate or to stop the pump when the delivery rate is below or exceeds a preset level.